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Monday, August 18, 2014

DAMA annual modulation explained without invoking dark matter

Physicists have plenty evidence for the existence of dark matter, matter much like the one we are made of but that does not emit any light. However, so far all this evidence comes from the gravitational pull of dark matter, which affects the motion of stars, the formation of structures, and acts as a gravitational lens to bend light, all of which has been observed. We still do not know however what the microscopic nature of dark matter is. What is the type of particle (particles?) that it is constituted of, and what are its interactions?

Few physicists today doubt that dark matter exists and is some type of particle which has just evaded detection so far. First, there is all the evidence for its gravitational interaction. Add to this that we don’t know any good reason why all matter should couple to photons, and on this ground we can actually expect the existence of dark matter. Moreover, we have various candidate theories for physics beyond the standard model that contain particles which fulfil the necessary properties for dark matter. Finally, alternative explanations, by modifying gravity rather than adding a new type of matter, are disfavored by the existing data.

Not so surprisingly thus, dark matter has come to dominate the search for physics beyond the standard model. We seem to be so very close!

Infuriatingly though, despite many experimental efforts, we still have no evidence for the interaction of dark matter particles, neither among each other nor with the matter that we are made of. Many experiments are searching for evidence of these interactions. It is the very nature of dark matter – it interacting so weakly with our normal matter and with itself – which makes finding evidence so difficult.

One observation being looked for is decay products of dark matter interactions in astrophysical processes. There are presently several observations, such as the Fermi γ-ray excess or the positron excess, whose astrophysical origin is not presently understood and so could be due to dark matter. But astrophysics combines a lot of processes at many energy and density scales, and it is hard to exclude that some signal was not caused by particles of the standard model alone.

Another type of evidence that is being sought after comes from experiments designed to be sensitive to the very rare interaction of dark matter with our normal matter when it passes through the planet. These experiments have the advantage that they happen in a known and controlled environment (as opposed to somewhere in the center of our galaxy). They experiments are typically located deep underground in old mines to filter out unwanted types of particles, collectively referred to as “background”. Whether or not an experiment can detect dark matter interactions within a certain amount of time depends on the density and coupling strength of dark matter, and so also on the type of detector material.

So far, none of the dark matter searches has resulted in a statistically significant positive signal. They have set constraints on the coupling and density of dark matter. Valuable, yes, but frustrating nevertheless.

One experiment that has instilled both hope as well as controversy among physicists is the DAMA experiment. The DAMA experiment sees an unexplained annual modulation in the event rate at high statistical significance. If the signal was caused by dark matter, we would expect an annual modulation due to our celestial motion around the Sun. The event rate depends on the orientation of the detector relative to our motion and should peak around June 2nd, consistent with the DAMA data.

There are of course other signals that have an annual modulation that cause reactions with the material in and around the detector. Notably there is the flux of muons which are produced when cosmic rays hit the upper atmosphere. The muon flux however depends on the temperature in the atmosphere and peaks approximately 30 days too late to explain the observations. The DAMA collaboration has taken into account all other kinds of backgrounds that they could think of, or that other physicists could think of, but dark matter remained the best way to explain the data.

The DAMA experiment has received much attention not primarily because of the presence of the signal, but because of the physicists’ failure to explain the signal with anything but dark matter. It adds to the controversy though that the DAMA signal, if due to dark matter, seems to lie in a parameter range already excluded by other dark matter searches. Then again, this may be due to differences in the detectors. The issue has been discussed back and forth for about a decade now.

All this may change now that Jonathan Davis from the University of Durham, UK, in a recent paper demonstrated that the DAMA signal can be fitted by combining the atmospheric muon flux with the flux of solar neutrinos:

Fitting the annual modulation in DAMA with neutrons from muons and neutrinos
Jonathan H. Davisarxiv:1407.1052

The neutrinos interact with the rock surrounding the detector, thereby creating secondary particles which contribute to the background. The strength of the neutrino signal depends on the Earth’s distance to the sun and peaks around January 2nd. In his paper, Davis demonstrates that for certain values of the amount of muons and neutrinos these two modulations combine to fit the DAMA data very well, as good as a dark matter explanation. And that is after he has corrected the goodness of the fit by taking into account the larger number of parameters.

Moreover, Davis discusses how the two possible explanations could be distinguished from each other, for example by analyzing the data for residual changes in the solar activity that should not be present if the signal was due to dark matter.

22 comments:

Oh my God! I thought to be a bit crazy. I did something very similar and numbers seem to give plausible result!I've considered our universe as a black hole and as a consequence I considered that the total mass of the universe shall affect the mass of each single object, as per Mach principle. The difference is that I assumed that precession and spin are couppled in the relativistic limit to normalize gravity and as a consequence a reversal effect of the centrifugal force that I added to the standard Newtonian acceleration.. Very happy to know that conformal gravity exist...

If this began by considering observations with the virial theorem then we can point to the inverse square laws as haunting similarity that has long suggested underlying unity of forces so expressed.Does this modify mass or gravity or products of the sometimes separate forces involved?Beyond this thus beyond the two primary physics also evoking a grounding in a unified theory we at least need fourth order quasi smooth Delta functions to establish curvature in linear systems as general vacuum structure change. That is, in these gravity matters a more general virial landscape idea is called for. Even a modification from the string standpoint.Even if evidence of dark matter particles are observed this analogy will not put at rest these deeper issues as if the more complete physics.Robert and Uncle AI sense these issues with their insistence or relevant ideas. The former as wider ideas of scale and the latter as a wider view of chirality.nemo your global of remote models are also relavant.Our graphs of calculus needs not only to be seen as flat earth and z axis gravity directed. Nor as simply a conformal iy axis.An ideal projective effect, a remote Maxwell demon or avoided singularity and superdetermined time where applies reflects Sabine's relavant questions and insights for the state or partial views of our new visions.

Such a proclamations are rather opportunist: when it becomes apparent, that the search for WIMPs faces dead end, then the hindsight is 20-20. But I think, that the scientists are getting fooled again - the DAMA signal can be still caused with dark matter component quite well - just in another form, than with WIMPs - as R.L.Oldershaw already noted.

Pardon, I meant to include I strongly agree with the general importance of Sabine's initial and terminal conditions which in a sense goes beyond our conventional ideas of Hamiltonian or other general models. For me these are all important in understanding biological system development.Work in many areas needs not be considered wasted as if dead ends of research commitments risked in the name of scientific exploration given the wider depth and span of context.Nor of what science cannot even indirectly speak do we judge. (I doubt if a God gave us brains we are expected not to use them or try to. ) Space seeks some ground as well we learn to fly in the white out of vertigo.

Your comment noted Markus. Also see http://arxiv.org/abs/1209.0563 and http://iopscience.iop.org/0256-307X/25/5/014 . But this article pimps the usual canard that dark matter must consist of particles. Even though they've never been found. Even though Einstein said a gravitational field is inhomogeneous space and "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy".

Fitting the annual modulation in DAMA with neutrons from muons and neutrinos Jonathan H. Davis arxiv:1407.1052

In acoustics this is what is labeled as fine tuning an acoustic piano.

The(muon analogous)(phase)modulations of the piano are superimposed against synthetically (neutron analogous)produced modulations to replicate the signal (frequency) of the note in need of tuning... analogous to the frequency of the DAMA signal.

The source for the signal needed for the piano is more earth bound than the signal source search of dark matter.

Speaking of scale, this article from Quanta magazine discusses how particle physicists are beginning to seriously explore the concept that scale is not absolute, but rather involves broken conformal symmetry.

Robert, "Well, it's a start, however humble it may be."A very good one I think.There is one thing that quite strikes me: As far as I know there are (only) three things that break scale:* Quadratic Higgs potential* Einstein gravity* Cosmological constant These correspond with the 3 biggest problems in fundamental physics:* Hierarchy problem* Nonrenormalizability of gravity* Cosmological constant problemAll these three things come with a dimension. Why not (quantum) generate the dimension like in QCD ? The magic word there is "dimensional transmutation".The price to pay though is that at short distances Einstein gravity cannot be the answer.

Look to Nature, not to mathematics or to past theoretical models, but rather to the more or less directly observable physical world of actually existing systems. It is there that you will find the lasting answers to your questions.

Expect that the answers will at first confound you and seem "impossible". Then think again more deeply.

I hate to bore everyone to death with my theory of Horizons, as regarding Dark Matter, since Dark Matter could be a bunch of things. Sheldon Glashow once had a lecture in which he thought that Dark Matter could be from Neutron Star Explosions, Say if you had Deuterium with 2 Neutrons, and Tritium with 3 N, and in Nuetron Stars you could have 4N, 500N, etc. So Dark matter would be very unstable, but would come to Earth in the Rain, and could be found at the bottom of the Ocean (since it is heavy). In my model of the Horizon, the Surface of Space Time has us on one side and Potential Energy (which turns into Quantum Mechanics at the Surface) on the other side. The Potential Energy can have mass (mgh, etc., but of course is Generally taken to be imaginary, unless very near the surface, in say Newtonian Mechanics). So the Universe has a lot of Potential Energy, has to be a part of Dark Matter, since it could turn into the top quark etc. Once again I would like to point out that some parts of theory are great, some ok, some just plain wrong. I liked Sheldon Glashow's idea, but many people have told me it was pure nonsense and he could not have possibly said that (I was there taking notes). I would like to point out that the speed of light is probably higher in Quantum Mechanics (as Feynman pointed out) just to get some converts.

Richard, I am not trying to dismiss your insights and intuitions off hand, you have profound things to say.I posted this to somewhere else but it applies in general:

It seems reasonable to imagine these speculations apply some place in the big picture of things in say the truly supernatural. But with the lack of a more general unified physics what may appear testable after all suggests a better model needed that it finds coherence's and closure as the natural. While these thoughts are of the highest order the profound description of such mechanisms fail to directly communicate being hamstrung by inadequate terms and the limited view where a sense of truth felt by this view just seems well grounded as complete.